A joint within the human body forms a juncture between two or more bones or other skeletal parts. The ankle, hip, knee, shoulder, elbow and wrist are just a few examples of the multitude of joints found within the body. As should be apparent from the above list of examples of joints, many of the joints permit relative motion between the bones. For example, the motion of sliding, gliding, hinge or ball and socket movements may be had by a joint. For example, the ankle permits a complicated movement, including a hinge movement, the knee allows for a combination of gliding and hinge movements and the shoulder and hip permit movement through a ball and socket arrangement.
The joints in the body are stressed or can be damaged in a variety of ways. For example, the gradual wear and tear is imposed on the joints through the continuous use of a joint over the years. The joints that permit motion have cartilage positioned between the bones providing lubrication to the motion and also absorbing some of the forces direct to the joint. Over time, the normal use of a joint may wear down the cartilage and bring the moving bones in a direct contact with each other. In contrast, in normal use, a trauma to a joint, such as the delivery of a large force, from an accident for, example, an automobile accident, may cause considerable damage to the bones, the cartilage or to other connective tissue such as tendons or ligaments.
Arthropathy, a term referring to a disease of the joint, is another way in which a joint may become damaged. Perhaps the best known joint disease is arthritis, which is generally referred to a disease or inflammation of a joint that results in pain, swelling, stiffness, instability, and often deformity.
There are many different forms of arthritis, with osteoarthritis being the most common and resulting from the wear and tear of a cartilage within a joint. Another type of arthritis is osteonecrosis, which is caused by the death of a part of the bone due to loss of blood supply. Other types of arthritis are caused by trauma to the joint while others, such as rheumatoid arthritis, Lupus, and psoriatic arthritis destroy cartilage and are associated with the inflammation of the joint lining.
In the human elbow, three degrees of freedom are present. These are flexion-extension, varus-valgus carrying angle and axial rotation.
Various elbow prosthesis have been constructed as a replacement for the natural human elbow. The two basic types of elbow prosthesis known in the prior art are semi-constrained and unconstrained. In semi-constrained prosthesis, the prosthetic joint is held together mechanically, by components of the prosthesis. Such devices are shown, for example, in U.S. Pat. No. 5,376,121 to Huene et al., U.S. Pat. No. 3,708,805 to Scales, et al., U.S. Pat. No. 3,939,496 to Ling, et al., and U.S. Pat. No. 4,224,695 to Grundei, et al. In an unconstrained device, the prosthetic device is held together by the patient's natural soft tissues. Such a device is shown in U.S. Pat. No. 4,293,963 to Gold, et al.
In each of these devices, one portion of the prosthesis is implanted in the humerus of the patient and the other portion is implanted in the ulna. The two portions then mate in some manner to allow articulation of the joint. In the '695 patent to Grundei, et al., an additional portion of the prosthesis is implanted in the radius of the patient.
A surgeon may not always know prior to beginning an operation whether a patient would be better served by a semi-constrained or unconstrained elbow prosthesis. Thus, it would be desirable to provide an elbow prosthesis that may be utilized in either the semi-constrained or unconstrained manner.
It may also be necessary to convert an unconstrained elbow prosthesis to a semi-constrained one, or vice versa, after implantation and use for a period of time. In order to do so, it is typically necessary to remove the portion of the prosthesis implanted in the humerus and ulna and to replace the entire prosthesis with either the semi-constrained or unconstrained variety.
Prosthetic elbows currently marketed typically can be implanted to operate in one of two ways. These two ways are an unconstrained or unlinked manner and the other way is a semi-constrained or linked manner. Unconstrained prosthetic elbows are more generally indicated for osteoarthritic or post traumatic patients with strong soft tissues about the elbow. Such patients have joints with surfaces that are arthritic and painful.
Typically, unconstrained elbows are designed with, for example, a metal humeral articulating surface and a polyethylene ulnar articulating surface. Each of these components have matching convex and concave surfaces, respectively.
Alternatively, semi-constrained prosthesis are used with inflammatory disease. The inflammatory disease results in the patient having weaker soft tissue and significant bone erosion. The weaker soft tissue and bone erosion makes the use of an unconstrained elbow more difficult in that the soft tissues are not of sufficient strength to properly contain the prosthetic components in contact with each other. A semi-constrained prosthesis uses a linkage pin at the elbow axis of rotation. The progression of osteoarthritis and other joint diseases may create a situation in which a patient first implanted with a unconstrained elbow prosthesis may, due to further loss of soft tissue, require the use of a semi-constrained prosthesis. This need for a different prosthesis may create a significant issue for the patient. The removal of particularly the stem portions of the prosthesis after being implanted for some time is difficult.
A product sold as the Acclaim Elbow™ sold by DePuy Orthopaedics, Inc., Warsaw, Ind. has been designed to attempt to alleviate at least partially the problem of inter-operatively converting from an unconstrained elbow to a semi-constrained elbow. The Acclaim Elbow™ can be more readily understood by reference to U.S. Pat. No. 6,027,534 and No. 6,290,725 incorporated herein in their entireties by reference.
While the Acclaim Elbow™ permits the conversion from an unconstrained elbow to a semi-constrained elbow without removing the entire prosthesis from the patient, the use of the Acclaim Elbow™ makes use of an axis pin mechanism for preventing dislocation and positioning of the axis of articulation. The Acclaim Elbow™ requires substantial amounts of condylar bone to be removed if the pin poly axis assembly wears and needs replacement.
The current Acclaim Elbow™, as well as other competitive elbow prosthesis, have a shape and configuration that may not be ideally suited to each particular patient's anatomy in that a patient, depending on gender and size, may have a bone structure that is not well suited to available implants.
Current elbow prosthesis have configurations that provide for complicated components for which the cost of manufacturing may be quite high.
Currently marketed elbow prosthesis make use of a locking axis pin as the main element of articulation for the semi-constrained form of the elbow prosthesis. Elbow prosthesis also include drilling techniques for condyles of the bone for removal of the poly/pin assembly. Such removal of bone to permit the removal of a prosthesis may severely weaken the supracondylar regions of the humerus. Such bone removal may weaken the support structure for the prosthesis and may lead to earlier failure.